Again the technology isn't specific to electric cars. And I am a bit of a car geek. When you say "Just look at the underside of pretty much every car in existence." I assume you might not have actually looked closely at many of the German cars. Mercedes has been a major fan of aerodynamic optimization after flipping a couple LeMans cars... the CLA is a great example of a slippery car but their entire lineup outside the AMG variants have been made extra extra slippy beating out the Chevy Volt at the time. The humble Volkswagens optimized as well. Sure ICE vehicles with RWD and exhaust pipes can't be "perfectly smooth" underneath, but some manufacturers still optimize for what they have, which is in fact more "tech" than throwing a flat piece of plastic under the car and claiming to be technologically superior. If you look under most German cars, you will see they have in fact been optimizing under car aero since the early 2000's.
The hypermiling eco-tires may be great for fuel economy, but they just made the trade-offs we already knew and avoided and I wouldn't be surprised to learn that most car geeks would chose better performing tires over their eco-variety on replacement.
And the option to buy the under-powered, narrow wheel sub compact has been there... but in America, that's an economy car which is balancing lowest TCO rather than raw efficiency. BMW i8s, which chose technology over cost, didn't sell well at all. The economy sub-compact seems like an insane decision of necessity in a capitalist country without universal healthcare when you are sharing the road with drunks, meth heads, armed road ragers and speeding over-loaded pickup trucks.
Often times the technology which makes a car more efficient also makes them perform better which is why many of the Mercedes are aluminum and AHSS and Porsche historically experimented with putting a lot of magnesium in their cars. I have an e-class wagon because it was the most efficient AWD 7 passenger "utility vehicle" my research led me to at the time. It didn't shout it's economy/technology/efficiency at me, but it's definitely there and could carry 600Kg payload (which is more than the Toyota Seqoia) while consuming less than 9L/100km.
Again, the problem is not that the technology isn't there in an ICE vehicle, you just have to pay more than you are willing to pay for it in a system where the manufacturer is incentivized to not give it to you and /hope you don't notice or care/. Electric vehicles come with IN YOUR FACE technology because the most pervasive new entrant into the market needed a distinguishing factor or it would bust, and now everyone else needs to copy. You could buy an electric car that is basically an electric forklift with a lithium battery thrown into VW Golf (the e-Golf)... and it is a fantastic car that didn't sell well.